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Old April 20th, 2004, 01:36 PM   #1
United States

kailashmariappan is offline
Join Date: Mar 2003
Location: Eden Prairie, Minnesota, USA - 55344
Posts: 5
Hi! Wanted software tools for analyzing existing PLC programs


I need to analyze a very complex PLC program written years back
by an engineer who is no longer with us. The rung comments are too limited to understand the program. This is a RS Logix 5 file written for Allen Bradley's PLC 5.

It has about 90 files with many Sub routine jumps.

Is there any software tool which will help me to automatically generate the following documents straight from the PLC program. (In other words, a sort of reverse engineering).

1. Program flow chart which will provide a clear picture of how the various sub routine files are called from other program files.

This chart should depict under what conditions the scan will jump
from one file to the other.

2. Logic Flow chart which will provide schematic flow sequence
caused by JMP and LBL instructions.

The chart should depict under what conditions the scan will jump from one group of rungs to the other.

If there is no such tool in the market, is there someone who is interested to join hands with me to develop such a tool. (You should be good in VB and in RS Logix programming). This could be a great opportunity to help the control engineers community and earn a good financial reward too.

With regards
Eden Prairie, MN, USA.
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Old April 20th, 2004, 04:32 PM   #2
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dale1627 is offline
Join Date: Jul 2003
Location: East Tennessee
Posts: 152
You wouldn't by chance happen to work for a printing facility there would you?

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Old April 20th, 2004, 05:49 PM   #3
Mike Williams
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Mike Williams is offline
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Join Date: Jul 2002
Location: Alabama
Posts: 222
You could write your own code to "capture" the sequence.

Write the sequence into a flowchart.(they do sell a pencil here and there).
Mike Williams
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Old April 21st, 2004, 03:17 AM   #4
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JesperMP is offline
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Location: Copenhagen.
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Good luck, see you in 5 years !


it would be bit hard but not impossible to write a program that shows how the JMPs and JSRs handle the scanning of the program code.
The use of this is a bit limited though. It doesnt tell you what the code actually does when it is scanned. So it doesnt provide a functional flow-chart.
And you allready have part of the above in the XREF list.

It would be IMPOSSIBLE to automatically generate a FUNCTIONAL flow-chart based on existing PLC5 code.
This because part of the functional program flow is also done by triggering individual rungs by means of a variety of conditions.
Some programs are made in a "loose" or even "spaghetti-like" manner. Such programs can be hard to figure out for a human, and impossible for a computer program.
Some programs are based on "state machines". One could think that it would be possible to automatically generate a flow chart for such programs. But sadly, there is no standard way to make state based programs, even though methods are allways similar.

The opposite would be possible:
To create PLC5 code bases on a predefined state-based flow chart.
See my profile interests for Q&A
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